|SREL Reprint #0853|
Studies on the Population Biology of Diplostomulum Scheuringi in a
Thermally Altered Reservoir
M. Aho, Joseph W. Camp, and Gerald W. Each
The prevalence and mean enfrapopulation density of Diplostomulum
metacercariae were monitored for 53 mo in populations of mosquitofish, Gambusia
affinis, located in ambient and thermally altered locations in Par Pond,
a 1,012-ha cooling reservoir located on the Savannah River Plant near Aiken,
South Carolina. Except fr six
monthly sampling periods, prevalence of D. scheuringi remained
> 75% at the ambient temperature station; peak prevalences occurred in late
summer and early fall, then declined in late winter and spring.
Mean densities at the ambient station varied significantly over the
course of the study; seasonal peaks occurred in late summer and fall, and lowest
densities in spring. Seasonal prevalence at the heated site paralleled that which
occurred at the ambient station during the initial 28 mo, but over the last 25
mo, prevalence varied erratically. Mean
densities of D. scheuringi fluctuated significantly at the heated
site during the 53 mo, but a distinct seasonal pattern was not apparent.
A significant linear decrease in mean density was observed during the
final 30 mo of the study. During 33
of the 53 mo, densities of metacercariae were not significantly different at the
two sampling stations. During 17 of
the 20 mo, when they were significantly different, densities were highest at the
ambient temperature site. The
decline in prevalence and density at the thermally altered station during the
last 30 mo may have resulted from changes in parasite transmission dynamics that
were caused by temperatures fluctuating rapidly over wide ranges, or by changes
in foraging or nesting behavior of the definitive host, which would reduce the
numbers of infective agents being dispersed in the habitat.
The prevalence and density of D. scheuringi were compared in four,
arbitrarily chosen, size classes of mosquitofish in the two areas of the
reservoir over one 12-mo period. Both
density and prevalence were affected most in the largest (>36mm) and smallest
15-25mm) size classes in the ambient location during late winter and early
spring; prevalence declines among all size classes of mosquitofish in the
thermally altered station during winter and spring.
The various seasonal changes in parasite population dynamics at both
stations were attributed to a combination of seasonal variation I cercarial
shedding from infected snails, recruitment of metacercariae, and to seasonal
patterns of birth and mortality of the short-lived mosquitofish.
At the heated station, periods of cercarial shedding and metacercarial
recruitment were altered by thermal effluent that also reduced the normal life
expectancy of mosquitofish, thereby further modifying the population biology of
SREL Reprint #0853
Aho, J.M., J.W. Camp, and G.W. Esch. 1982. Long term
studies on the population biology of Diplostomulum scheuringi in
a thermally altered reservoir. Journal of Parasitology 68:695-708.